The invention relates to a liquid dispensing device comprising at least one piston pump, which sucks liquid to be dispensed from a container in a filling cycle and applies said liquid to a target in an emptying cycle and which is driven by an actuator comprising an actuating means that is arranged to move a piston rod between two extreme positions, and a gripper attached to the actuating means, which gripper is able to engage with the piston rod so as to move it along with the actuating means. The extreme positions refer to the two positions between which the piston is shifted in the cylinder of the piston pump. These positions need not correspond to those of empty and full piston pumps.
A dispensing device as described above is known from U.S. Pat. No. 5,567,122. The gripper, which in this case is a pin moved by a solenoid, is arranged to move along with the actuator. To retain the engagement of the gripper requires continuous power supply to the solenoid. Because the gripper moves with the actuator, the power supply must be arranged by means of flexible cables or the like arrangements. If the apparatus includes a plurality of piston rods, like the paint toning machine which is intended to be a particular application of the present invention, the gripping arrangement of the U.S. Pat. No. 5,567,122 is difficult, complicated and space-consuming.
As stated above, dispensing devices of the invention are used, in particular, for dispensing colour paste. In some known dispensing devices the actuating means of the actuator driving the piston pump is continuously in cooperation with the piston rod, and as the actuating means moves so does the piston rod. The cooperation between the piston pump and the actuator is advantageous in a dispensing device comprising one piston pump, but when a plurality of piston pumps are driven by one and the same actuator, the situation is always such that only some of the piston pumps are desired to supply colour paste. Because the actuator is coupled to all piston rods, it is not possible to stop the movement of the idle piston pumps but liquid dispensing from said pumps must be prevented by valve operations.
A problem with the above-described arrangement is that the idle piston pumps move unnecessarily with the actuator, which wastes energy and results in unnecessarily fast wearing of the parts. Complicated valve arrangements may also cause problems, because the automation system thereof should take care of stopping and restarting the liquid dispensing.